Pulse generating electrical circuit arrangements



' K. T. LIAN March 16, 1965- PULSE GENERATING ELECTRICAL CIRCUIT ARRANGEMENTS 2 Sheets-Sheet 1 Filed July 8. 1960 b 18 D Va LOAD LOAD ,1

INVENTOR W M; I Y

A'ITORNEYS kvmm n NS M359.

March 16, 1965 K. T. LIAN 3, 08

PULSE GENERATING ELECTRICAL CIRCUIT ARRANGEMENTS Filed July 8. 1960 2 Sheets-Sheet 2 3/ LOAD/ .35 33 32 O L I ll 37 3a 33 3/ 34 PULSE LOAD/ saunas 2 ATTORNEYS United States Patent 3,174,108 PULSE GENERATING ELECTRICAL CIRCUIT ARRANGEMENTS Kenneth T. Lian, Wantagh, N.Y., assignor to Polytechnic Institute of Brooklyn, Brooklyn, N.Y., a corporation of New York Filed July 8, H60, Ser. No. 41,664 13 Claims. (Cl. 3328-76) This invention relates to pulse forming and shaping circuits and more particularly to circuit arrangements for producing pulses of short duration but extremely high energy as required by modern radar systems and also by various fusion projects.

The primary limiting factor in the switching of high energy pulses at this time appears to be the life of electrodes. A good many radar systems use rotary spark gaps, vacuum tubes .or gas tubes as switching elements and in each instance the higher the pulse energy level is increased, the shorter becomes the life of the electrodes involved. Electrode replacement in the fusion projects to date presents no particular problem because so far only single shot transients are being used and electrode replacement therefore is no hindrance to experimenters in this field. Whenever repetitive higher energy level pulses are required, however, as in high power radar systems, electrode replacement is a definite hindrance and becomes a limitation on the number of hours of continuous operation of apparatus of tln's kind. Prior art attempts at electrode elimination for high energy pulse circuits capable of continuous operation include cascaded chains of saturable reactor stages with shunt condensers. The difficulty with the saturable reactor type circuit is that while it can handle the power required, there are other limitations. Among these are the large volume of expensive iron required in the cores, together with the problem of mechanically supporting the laminations and the fact that with A.C. charging of line type pulsing systems inherent time jitter of the A.C. source precludes their use in low jitter systems. When plasma switches are substituted for saturable reactors, they may be externally synchronously controlled in order to compensate for time jitter of the source which of course -is not possible with saturable reactors. In the case of D.C. charging of line type pulsing systems both the saturable reactor circuits and the plasma switch circuits require electronic switches. However, in the case of the plasma switch, the jitter requirements on the electronic switch are far less severe since the plasma switch can itself be synchronized with an external signal.

Accordingly, it is the principal object of the present invention to provide a pulse forming and shaping circuit capable of providing extremely high energy level pulses and which is free of the aforementioned problems.

Electrode problems are eliminated by using plasma switches which are devoid of electrodes.

A complete understanding of the present invention may be had by reference to the following drawings in conjunction with the attached specification. In the drawings,

FIG. 1 is a schematic wiring diagram of a preferred embodiment of the present invention for A.C. charging of line type systems;

FIG. 2 is a inodification of the circuit arrangement shown in FIG. 1;

FIG. 3 shows a simplified form of a plasma switch;

FIG. 4 is a diagram showing typical wave forms encountered in the several stages of the apparatus shown for example in FIG. 1;

FIG. 5 is a circuit similar to FIG. 1 but modified for use with a D.C. source;

FIG. 6 is similar to FIG. 5 but with the switch in shunt with the load rather than in series;

3,174,193 Patented Mar. 16, 1965 FIG. 7 is a simplified version of the circuit of FIG. 5.

In general, the objects of the present invention are achieved by utilizing cascaded stages, each stage including a plasma switch and a condenser, and with the eascaded stages connected between a periodically varying source and the load or including an electronic switch if the source is D.C. In each stage, the plasma switch may be inseries with the load, and the condenser in shunt with the load, or the reverse may be true. In the case of D.C. charging systems, the electronic switch may be in series or shunt with the load.

Referring now to FIG. 1 of the drawings, which shows a preferred embodiment of the present invention in schematic form, a plurality of plasma switches 10 are serially connected with a load device 11 and an equal number of condensers 12 are connected in shunt with the load, one for each plasma switch. A source of alternating current preferably .but not necessarily sinusoidal, is shown connected to the input of the first stage through an inductor 14.

A simple form of electrodeless plasma switch is shown in FIG. 3. It comprises a torus 10a of glass or other suitable material filled with a gas at reduced pressure and this torus is linked with a laminated iron core represented as a ring 10b. With a primary winding 10c on the iron core, the gas filled torus 10a when ionized becomes in effect a single turn short-circuited secondary winding. While the actual shape of the gas filled member is subject to variation as well as the specific shape of the core, such variations will have no substantial effect on the use of a device in the circuit arrangement of the present invention. The initial ionization of the gas in the torus can be accomplished by means of the electric field caused by the rate of change of flux in'the iron core, or by external means, such as voltages across auxiliary electrodes, ionizing radiation, radio frequency signals and the like.

In order to prevent the occurrence of bidirectional pulses of twice the source frequency in the load circuit of for example FIGURE 1, it is necessary to apply a biasing to the core of at least the first plasma switch. Biasing circuits for this purpose are shown applied to each of the plasma switches of FIGURE 1. While the showing is schematic in this regard, each is identical and comprises a D.C. voltage source shown as a battery 15 connected in series with a reactor 16, a winding 17 inductively linked to the plasma switch core and a resistor 18.

Referring now to FIG. 4 of the attached drawings for a description of the operation of the circuit arrangement of FIG. 1, the sine wave input voltage is indicated by the curve A and the corresponding voltage on the condenser C by the curve B. As soon as the voltage on the condenser in the first stage has built up to a level determined by the inherent operating characteristics of the plasma switch of the first stage, the gas in the plasma switch ionizes and the energy of the condenser is transferred quite rapidly. The initiation of discharge of the condenser of the first stage initiates the charging of the condenser in the second stage and the voltage wave form for the condenser of the second stage appears at curve D. The process is repetitive through each of the stages and the voltage curves for the condensers in each stage are therefore represented in FIG. 4 by the wave forms B, C, and D. While the frequency of pulses delivered to the load is the same as the frequency of the input source, the power levels and the time duration of the pulse is quite diiferent from the sinusoidal input. As a typical operating schedule, if the period of the input sinusoidal voltage be considered as taking place in a time T, then the discharge of condenser C through its plasma switch takes place in a time equal to T divided by 10. The initiation of the discharge of each stage triggers the charging of the condenser in the succeeding stage so that the discharge time of each stage substantially equals the charging time for the succeeding stage. The discharge time of capacitor C in the second stage is equal to T divided by 100. The discharge time of capacitor C is of the order of T divided by 1,000 and this is the pulse delivered to the load. The pulse appearing at the load, therefore, is of a very high peak and average power and has a pulse width of the order of of the period of the input source. The wave shape of the load pulse will vary depending upon the characteristics of the load, and the curve E in FIG. 4 approximates the wave shape in the event that the load is primarily resistive rather than reactive.

Referring now to FIG. 2 of the attached sheet of drawings, it will be appearent to those skilled in the art that the only difference between FIGS. 1 and 2 is that the position of the condensers and plasma switches have been reversed in the circuit arrangement. This does not change in any way the basic mechanism by which the pulses are produced.

Referring now to FIG. 5 of the drawings, there is shown a two stage adaptation of the circuit of FIG. 1 for use with direct current voltage sources. The direct current source in this case is schematically indicated by a battery 30. The load 31 is connected in a series circuit which includes the plasma switch 32 and the condenser 33 in the same basic configuration as shown in FIG. 1. In order to obtain pulsed operation from a direct current source, it is necessary to include some sort of switching means in the supply circuit and such means are shown in this figure as comprising a grid controlled gaseous rectifier 34. In order to comply with the polarity of the source, the anode of the rectifier is connected to the positive side of the source through an inductance 35 and a diode 36 while the cathode of the rectifier is connected to the junction of the plasma switch 32 and the condenser 33 through a reactor 37. In order that the gaseous rectifier may act as a periodic switch, a small low energy-level triggering pulse source 38 is shown con-.

nected between the grid and cathode. The magnetic biasing circuit for the plasma switch is the same as in FIG. 1.

FIG. 6 shows a modification of the circuitry of FIG. 5, the principal difference being that the electronic switch 34 is placed in shunt rather than in series with the load. Here again the basic mechanism of pulse. generation remains the same.

Referring lastly to FIG. 7, this shows still another form of D.C. charging circuit which is a slight modification of the circuit of FIG. 5. Here the plasma switch 32, magnetic biasing circuit 15, 16, 17 and 18, load 31 and condenser 33 remain as before. The gaseous rectifier 34 however, has its cathode connected directly to the junction between the condenser 33 and plasma switch 32 and its anode connected through a reactor 35 to the D.C. source. This is therefore a single stage circuit.

From the foregoing description, it will be apparent to those skilled in the art that the net effect of plural cascaded stages of the present invention is to produce a very pronounced time compression of the pulses in each stage. The ultimate pulse delivered to the load is of extremely short duration compared to the period of the supply volt age. Since electrodes have been eliminated, the primary object of the invention has been achieved, and the circuits herein shown and described are capable of sustained operation at high energy levels.

While preferred embodiments have been herein shown and described, applicant claims the benefit of a full range of equivalents within the scope of the appended claims.

I claim:

1. A circuit arrangement for delivering a series of high power short duration pulses to a load device comprising:

a condenser;

a plasma switch, said switch comprising a ferro magnetic core having a primary winding thereon and a short-circuitable secondary Winding consisting of a closed hollow loop surrounding said core, and filled with an ionizable gas under low pressure;

means connecting said condenser and said primary winding in a closed loop series circuit with the load;

and means affording connection across one of said series circuit elements of a source of periodically varying potential.

2. An arrangement as defined by claim 1 in which said last mentioned means affords connection of a source of varying potential across said condenser element.

3. An arrangement as defined by claim 1 in which said last mentioned means affords connection of a source of varying potential across said plasma switch element.

4. An arrangement as defined by claim 1 and including means for supplying a biasing to the core of said plasma switch.

5. A circuit arrangement for delivering a series of high power short duration pulses toa load device comprising:

a condenser;

a plasma switch, said switch comprising a ferro magnetic core having a primary winding thereon and a short-circuitable secondary winding consisting of a closed hollow loop surrounding said core, and filled with an ionizable gas under low pressure;

a T connection in which the top of the T includes the following elements serially connected in the order named:

a reactance;

a switching means and said primary winding of said plasma switch, and in which the leg of said T comprises said condenser with one side connected to the top of the T between said primary winding and said switching means;

means affording connection of a load between the free end of said primary winding and the free end of said condenser;

means affording connection of a source of direct current between the free end of said condenser and the free end of said reactance;

and means for periodically actuating said switching means.

6. The combination of claim 5 in which said switching means comprises a thyratron normally biased to cut off, and means for periodically triggering said thyratron into conduction.

7. The combination of claim 5 and including means supplying a biasing to the core of said plasma switch.

8. A circuit arrangement for delivering a series of high power short duration pulses to a load device comprising: a first plurality of circuit elements serially connected with the load; a second plurality of circuit elements connected in shunt with the load, one located ahead of each of said first plurality of elements, one plurality being condensers and the other plurality being plasma switches each said plasma switch comprising a ferro magnetic core having a primary winding thereon and a short-circuitable secondary winding consisting of a closed hollow loop surrounding said core, and filled with an ionizable gas under low pressure; and means affording connection of a periodically varying source of voltage to that pair of said circuit elements most remote from the load.

9. The combination defined by claim 8 in which said serially connected circuit elements comprise plasma switches and said shunt elements comprise condensers.

10. The combination defined by claim 8 in which said serially connected circuit elements comprise condensers and said shunt elements comprise plasma switches.

11. The combination defined by claim 8 and including means for supplying a biasing M.M.F. to the core of at least one of said plasma switches.

12. A circuit arrangement for delivering a series of high power short duration pulses to a load device comprising: circuit elements including a plasma switch element and a condenser element connected in series with each other and with the load in a closed loop; an inductance; a grid controlled gaseous rectifier having its anode connected to one side of said inductance and its cathode connected to the junction between said circuit elements; means supplying the grid of said rectifier with a periodically varying source of triggering pulses; and means affording connection of a source of direct current voltage between the other end of said inductance and that side of said load which permits current flow in the order named, from said source, then said inductance, gaseous rectifier, one of said circuit elements, the load, and return to the source.

6 13. The combination as defined by claim 12 and including means for supplying a biasing M.M.F. to the core of said plasma switch.

References Cited by the Examiner UNITED STATES PATENTS 1,136,684 4/ 15 Ledwinka 315--248 1,534,251 4/25 Smith 315248 2,467,476 4/49 Hallmark 328-39 2,688,705 9/54 Fundingsland 32865 2,919,414 12/59 Nietzert 33187 2,942,191 6/60 Vhelty 328-67 2,961,557 11/60 Hubert 315248 r JOHN W. HUCKERT, Primary Examiner. 0

GEORGE N. WESTBY, ARTHUR GAUSS, Examiners. 

1. A CIRCUIT ARRANGEMENT FOR DELIVERING A SERIES OF HIGH POWER SHORT DURATION PULSES TO A LOAD DEVICE COMPRISING: A CONDENSER; A PLASMA SWITCH, SAID SWITCH COMPRISING A FERRO MAGNETIC CORE HAVING A PRIMARY WINDING THEREON AND A SHORT-CIRCUITABLE SECONDARY WINDING CONSISTING OF A CLOSED HOLLOW LOOP SURROUNDING SAID CORE, AND FILLED WITH AN IONIZABLE GAS UNDER LOW PRESSURE MEANS CONNECTING SAID CONDENSER AND SAID PRIMARY WINDING IN A CLOSED LOOP SERIES CIRCUIT WITH THE LOAD; AND MEANS AFFORDING CONNECTING ACROSS ONE OF SAID SERIES CIRUIT ELEMENTS OF A SOURCE OF PERIODICALLY VARYING POTENTIAL. 